1. Technical Field
The present disclosure relates to wireless communication devices and a wireless communications system including multiple wireless communication devices, and more particularly to a wireless communications system that uses multiple frequency bands (or just bands).
2. Description of the Related Art
In an unlicensed band such as 2.4-GHz band, for example, wireless communication devices can perform communication without the necessity to acquire a license. However, there is concern that increase in wireless communication devices that use unlicensed bands, such as sensor wireless systems, leads to an increase in the amount of traffic in those bands to the point of hindering communication. A method has been proposed in which wireless communication devices capable of communication on multiple channels are used and the channel being used is switched in the event of degradation in communication conditions. This method is effective when frequency allocation within bands is fixed such as in licensed bands; however, as diverse communication schemes are used in unlicensed bands and also devices other than wireless communication devices are present, switching of channels is not sufficient in some cases. Additionally, in a wireless communications system including a single host unit and multiple remote units, information on the destination channel is sent from the host unit to remote units. Accordingly, as the number of remote units increases, the burden on the host unit becomes high and the amount of traffic is increased.
Wireless communications systems are known that selectively use one of multiple bands in a wireless environment in which multiple wireless communication devices perform multiple wireless communication sessions concurrently. Systems of this type are disclosed in Japanese Unexamined Patent Application Publication Nos. 2013-085099, 2014-068134, and 2003-259434, for example.
The technique disclosed by Japanese Unexamined Patent Application Publication No. 2013-085099 enables effective changeover of the band being used in wireless communication among multiple wireless devices to another band in, for example, a smart utility network (SUN). This technique achieves dynamic switching of bands with a small amount of traffic by exchanging band switch requests, responses, and schedule information among wireless devices and switching the band based on the schedule information.
The technique disclosed by Japanese Unexamined Patent Application Publication No. 2014-068134 prevents a long interruption of communication when the frequency band being used for communication is automatically changed in, for example, a wireless LAN. According to the technique, a band switch request is sent from a remote unit to the host unit, which then switches the band based on a calculated time. Since this technique switches the band upon elapse of a certain time period after reception of a band switch request, communication is not interrupted for a long time at the time of band switching and no wasted time occurs.
The technique disclosed by Japanese Unexamined Patent Application Publication No. 2003-259434 selects a frequency band for communication that meets conditions from multiple frequency bands in, for example, mobile communication. In the technique, the availability of bands and the conditions of transmission channels are detected and bands are switched based on them. This technique enables selection of a better band as it employs channel conditions in addition to band availability.